1. Field
The present invention generally relates to electrical circuitry for delivering power to a load directly from a rectified AC voltage, and more particularly relates to delivering power to LED-based lighting products.
2. Background Art
Recently, there has been great interest in reducing the energy consumption of lighting sources, as well as in reducing the size and costs of the lighting sources while also increasing the lifetime of such products. Since it is well known that conventional incandescent light bulbs waste a significant amount of energy in the form of heat, alternatives to incandescent lighting are seen as a possible means of reducing energy consumption. Fluorescent lighting and light emitting diode (LED) lighting are two alternative forms of lighting.
An LED is a well-known semiconductor device comprising a PN junction that emits light when forward-biased. Conventional control circuits for LED-based lighting products typically consist of two circuit portions. A first one of the two circuit portions is an AC-to-DC converter. In some instances these AC-to-DC converters include power factor correction circuitry. A second one of the two aforementioned circuit portions is a current controller coupled to drive a plurality of LEDs in series, in parallel, or in both series and parallel, depending on the desired wattage, voltage, and/or light output. Conventional versions of these circuits require various nodes therein to operate at relatively high voltages, and further require the presence of capacitors having high capacitance values. There are a number of different types of capacitor components; however, the only practical type of capacitors for the requirements mentioned above are electrolytic capacitors.
Unfortunately, incorporating electrolytic capacitors into these circuits limits the reliability of LED products generally. In particular, electrolytic capacitors tend to be the electrical component that is among the first to fail in an LED-based lighting product.
What is needed are low-cost, long-life circuits, without electrolytic capacitors, suitable for delivering power to an LED-based lighting product.